Synthesis and properties of 2,7-phenylethenyl-and benzoxazol-2-ylethenyl N-ethylcarbazole derivatives

Article abstract of DOI:10.1134/S1070428010080130

A number of new symmetrically and unsymmetrically substituted 2,7-phenylethenyl and benzoxazol-2-ylethenyl N-ethylcarbazole derivatives were synthesized by successive Wittig and Knoevenagel olefinations of 9-ethylcarbazole-2,7-dicarbaldehyde. The resulting compounds showed strong photoluminescence in the blue region. The spectral parameters of unsymmetrically substituted 9-ethylcarbazoles with a donor-donor-acceptor conjugation type are determined by intramolecular interaction in the donor-acceptor fragment. Pleiades Publishing, Ltd., 2010.

Full text of DOI:10.1134/S1070428010080130

ISSN 1070-4280, Russian Journal of Organic Chemistry, 2010, Vol. 46, No. 8, pp. 1185–1191. © Pleiades Publishing, Ltd., 2010.
Original Russian Text © V.K. Ol’khovik, A.G. Baran, 2010, published in Zhurnal Organicheskoi Khimii, 2010, Vol. 46, No. 8, pp. 1184–1190.
Synthesis and Properties of 2,7-Phenylethenyl-
and Benzoxazol-2-ylethenyl N-Ethylcarbazole Derivatives
V. K. Ol’khovik and A. G. Baran
Institute of New Materials Chemistry, National Academy of Sciences of Belarus,
ul. F. Skoriny 36, Minsk, 220141 Belarus
e-mail: slavol@ichnm.basnet.by
Received May 27, 2009
Abstract—A number of new symmetrically and unsymmetrically substituted 2,7-phenylethenyl and benzoxa-
zol-2-ylethenyl N-ethylcarbazole derivatives were synthesized by successive Wittig and Knoevenagel olefina-
tions of 9-ethylcarbazole-2,7-dicarbaldehyde. The resulting compounds showed strong photoluminescence in
the blue region. The spectral parameters of unsymmetrically substituted 9-ethylcarbazoles with a donor–donor–
acceptor conjugation type are determined by intramolecular interaction in the donor–acceptor fragment.
DOI: 10.1134/S1070428010080130
In the past decades much attention has been given
to possible applications of organic molecules as molec-
ular conductors, switchers, field-effect transistors, or-
ganic light-emitting diodes, etc. [1–3]. An advantage of
organic electroactive and photoactive materials over
inorganic is the possibility for directed tuning of
molecular properties via relatively simple chemical
modifications. Poly-π-conjugated carbazole derivatives
constitute an extensively studied group of organic
compounds which possess a good (predominantly
hole) conductivity and high stability and display
strong photo- and electroluminescence [4]. Therefore,
they attract interest as promising materials for the
design of organic light-emitting devices [5–7]. Most
publications in this field are concerned with the syn-
thesis and properties of symmetrical 3,6- or 2,7-di-
substituted polyconjugated oligomeric and polymeric
carbazole derivatives.
In the present article we report on the synthesis and
spectral parameters of new unsymmetrically substi-
tuted poly-π-conjugated carbazole derivatives having
electron-donating and electron-withdrawing groups in
positions 2 and 7. Such compounds may be regarded as
donor–donor–acceptor (D–D–A), donor–donor–donor
(D–D–D), or acceptor–donor–acceptor (A–D–A) poly-
conjugated systems. As electron-acceptor fragment we
introduced benzoxazole ring which was conjugated
with the carbazole core via ethylene bridge. The other
side chain was phenylethenyl or 4-fluorophenylethenyl
substituent.
We believed that the most practical synthetic ap-
proach to such system should be based on successive
Wittig and Knoevenagel olefinations of appropriate di-
aldehyde. As starting compound we used N-ethylcar-
bazole-2,7-dicarbaldehyde (IV) which was synthesized
Scheme 1.
MeO
OMe
MeO
OMe
EtBr
77%
N
H
N
Et
II
O
O
O
O
I
O
O
HO
OH
LiAlH4
89%
PCC
74%
N
N
Et
IV
Et
III
1185

OL’KHOVIK, BARAN
1186
Scheme 2.
O
PPh3 Cl–
R
IV
+
N
63–68%
R
Et
V, VI
VII, VIII
O
Me
O
N
IX
R
N
Et
88–91%
X, XI
R
V
N
92%
Et
XII
O
O
IX
N
N
Et
XIII
IV
R
R
V, VI
N
Et
XIV, XV
V, VII, X, XIV, R = H; VI, VIII, XI, XV, R = F.
in three steps from dimethyl 9H-carbazole-2,7-dicar-
boxylic acid (I) as shown in Scheme 1. Alkylation of
the carbazole nitrogen atom was performed with
a view to enhance electron-donor power of the carba-
zole core and improve the solubility of the resulting
polyconjugated systems. Consistent effects of two
electron-withdrawing ester groups in positions 2 and 7
of the carbazole ring considerably reduced the basicity
of the carbazole nitrogen atom, and N-ethyl derivative
II was obtained in acceptable yields only by prolonged
heating of 9H-carbazole I in xylene in the presence of
a large excess of ethyl bromide and potassium car-
bonate. The alkylation of I with the use of strong
bases, e.g., potassium tert-butoxide, in aprotic polar
solvents was accompanied by side transesterification.
lithium tetrahydridoaluminate in tetrahydrofuran. The
subsequent oxidation of diol III to the corresponding
dialdehyde IV was performed using pyridinium
chlorochromate (PCC). This reaction can be carried
out in methylene chloride, chloroform, 1,2-dichloro-
ethane, or dioxane with equal success. With a view to
obtain unsymmetrically substituted carbazoles X–XII,
phenylethenyl and benzoxazolylethenyl groups were
introduced into the carbazole core in two steps with
necessary isolation of intermediate monoaldehydes
VII and VIII (Scheme 2). An attempt to synthesize
compound XII by reaction of dialdehyde IV with
an equimolar mixture of phosphonium salts V and VI
according to Wittig gave a mixture of symmetrically
and unsymmetrically substituted carbazole derivatives
XII, XIV, and XV. Monosubstituted carbazoles VII
and VIII were obtained by reaction of dialdehyde IV
Dialdehyde IV was synthesized in two steps. The
ester groups in II were reduced to hydroxymethyl with
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 46 No. 8 2010

SYNTHESIS AND PROPERTIES OF 2,7-BIS(PHENYLETHENYL)- ...
1187
with the corresponding phosphonium salts. Coupling
of IV with ylide generated from phosphonium salt V
or VI by the action of potassium tert-butoxide in tetra-
hydrofuran was characterized by high stereoselectivity,
and compounds VII and VIII were formed exclusively
as trans isomers. Electron-acceptor benzoxazole group
was introduced by condensation of monoaldehydes
VII and VIII with 2-methylbenzoxazole (IX) in
DMSO in the presence of potassium tert-butoxide. The
yields of unsymmetrically substituted carbazoles X and
XI isolated by column chromatography were 55–62%
calculated on the initial dialdehyde IV. By two con-
secutive Wittig reactions we synthesized unsymmet-
rically substituted 9-ethyl-2-[(E)-2-(4-fluorophenyl)-
ethenyl]-7-[(E)-2-phenylethenyl]-9H-carbazole (XII)
in an overall yield of 63%. The condensation of alde-
hyde VIII with phosphonium salt V was also highly
stereoselective, and the major product was trans,trans
isomer XII.
zole core. δ, ppm: 7.44 d (2H, 3-H, 6-H), 7.82 s and
7.84 s (1H each, 1-H, 8-H), 8.12 d (2H, 4-H, 5-H).
Protons at the exocyclic double bonds gave rise to
a multiplet at δ 7.38–7.43 ppm (4H); taking into ac-
count the above stated, the most probable configura-
tion of the vinylic fragments in XII is trans (E). The
chemical shifts of protons in the unsubstituted phenyl
ring are 7.28 (t, 1H, p-H), 7.49 (t, 2H, m-H), and
7.66 ppm (d, 2H, o-H). Protons in the p-fluorophenyl
ring displayed coupling not only with each other but
also with the fluorine nucleus, δ, ppm: 7.25 d.d (2H,
m-H), 7.70 d.d (2H, o-H). In the IR spectrum of XII,
stretching vibrations of the exocyclic double C=C
bonds gave rise to absorption at 1600 cm–1.
In order to estimate the effect of unsymmetrical
structure of compounds X–XII on their spectral prop-
erties we also synthesized the corresponding symmet-
rically substituted derivatives, namely 2,7-bis[(E)-2-
(benzoxazol-2-yl)ethenyl]-9-ethyl-9H-carbazole
(XIII), 2,7-bis[(E)-2-phenylethenyl]-9-ethyl-9H-carba-
zole (XIV), and 2,7-bis[(E)-2-(4-fluorophenyl)ethen-
yl]-9-ethyl-9H-carbazole (XV). Compounds XIII–XV
were synthesized in one step from aldehyde IV as
shown in Scheme 2 (by Knoevenagel or Wittig reac-
tion). Compounds XIII was obtained in 76% yield
by condensation of aldehyde IV with 2.5 equiv of
2-methylbenzoxazole in the presence of potassium
tert-butoxide in DMSO. Symmetrically substituted
2,7-bis[(E)-2-phenylethenyl]carbazoles XIV and XV
were prepared by reaction of dialdehyde IV with
2.5 equiv of the corresponding phosphonium ylide in
THF; the yields were 64–68%.
The results showed insignificant effect of electro-
negative fluorine atom on the spectral parameters of
unsymmetrically substituted carbazole derivatives.
Compounds like D–D–A (X, XI) displayed photo-
luminescence in the blue region with its maximum at
λ 471–472 nm. Likewise, the emission maximum of
compound XII weakly depended on the substituent
in the benzene ring of the phenylethenyl fragment
(λmax 434 nm). No appreciable differences in the posi-
tion of absorption and emission maxima were also
observed between compound XII and symmetrically
substituted derivatives XIV and XV. The blue shift
(Δλ = 35–38 nm) in the luminescence spectra of
D–D–D (XII, XIV, XV) and D–D–A type compounds
(X, XI) is likely to result from replacement of the
electron-deficient benzoxazole fragment by phenyl
group, while the size of the π-conjugation chain in
these compounds remained almost unchanged.
The structure of compounds X and XI was deter-
1
mined on the basis of their H NMR, IR, and mass
spectra. Signals from protons in the two (E)-ethenyl
1
groups appear in the H NMR spectra as four doublets
at δ 7.42, 7.51, 8.02, and 8.18 ppm with coupling
3
constants J of 16.0–16.5 Hz. The chemical shifts of
protons in the benzoxazole fragment are as follows,
δ, ppm: 7.40 t and 7.42 t (1H each, 5-H or 6-H), 7.74 d
and 7.76 d (1H each, 4-H or 7-H). Signals from pro-
tons in the benzene ring of compound X were observed
at δ 7.25, (t or d.d, 2H, m-H)), 7.71 (d.d, 2H, o-H), and
1
7.29 ppm (t, 1H, p-H). In the H NMR spectrum of
para-fluorophenylethenyl-substituted compound XI,
additional couplings between the ortho- and meta-
protons, on the one hand, and fluorine nucleus, on the
other, were observed with constants JHF of 9.0 and
5.5 Hz, respectively. Analogous couplings were found
in the 19F NMR spectrum. The unsymmetrically sub-
stituted carbazole fragment gave rise to six proton
signals at δ, ppm: 7.43 d (1H, 6-H), 7.51 d and 7.65 d
(1H each, 4-H, 5-H), 7.85 s (1H, 8-H), 8.16 d (1H,
3-H), 8.18 s (1H, 1-H). In the IR spectra of X and XI
absorption bands corresponding to stretching vibra-
tions of the exocyclic double C=C bonds were ob-
served at 1640–1647 cm–1.
1
The H NMR spectral pattern of compound XII
also demonstrated unsymmetrical substitution in the
carbazole core (four groups of signals were present).
However, taking into account similar electronic effects
of (E)-2-phenylethenyl and (E)-2-(4-fluorophenyl)-
ethenyl substituents, different chemical shifts were
found only for the 1-H and 8-H protons in the carba-
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 46 No. 8 2010

OL’KHOVIK, BARAN
Compounds X and XI having one electron-with-
1188
1250, 1237, 1220, 1210, 1150, 1143, 1103, 1067, 1000,
957, 943, 880, 837, 830, 793, 767. 1H NMR spectrum,
δ, ppm: 1.44 t (3H, CH2CH3, J = 7.0 Hz), 3.94 s (6H,
CH3), 4.55 q (2H, NCH2, J = 7.2 Hz), 7.84 d (2H, 3-H,
6-H, J = 8.0 Hz), 8.14 s (2H, 1-H, 8-H), 8.22 d (2H,
4-H, 5-H, J = 8.0 Hz).
drawing side-chain group absorb at longer wavelengths
as compared to symmetrically substituted 2,7-bis[(E)-
2-(benzoxazol-2-yl)ethenyl]-9-ethyl-9H-carbazole
(XIII, A–D–A), and the red shift reached 20.5 nm.
However, the difference in the photoluminescence
maxima of benzoxazole-containing compounds X, XI
and XIII was not large, Δλ = 4–6 nm. Presumably, the
reason is that the effect of the donor–acceptor frag-
ment, i.e., (E)-2-(benzoxazol-2-yl)ethenylcarbazole
chromophore, in compounds X and XI on the position
of the emission maximum is much stronger than the
effect of the (E)-2-phenylethenyl group.
(9-Ethyl-9H-carbazole-2,7-diyl)dimethanol (III).
Dimethyl 9-ethyl-9H-carbazole-2,7-dicarboxylate (II),
311 mg (1.0 mmol), was dissolved in anhydrous THF,
350 mg (~9.0 mmol) of lithium tetrahydridoaluminate
was added, and the mixture was stirred for 1 h at room
temperature and then heated for 2 h under reflux, the
progress of the reaction being monitored by TLC.
When the reaction was complete, ethyl acetate and
50% aqueous potassium hydroxide were added until
aluminum hydroxide separated. The precipitate was
filtered off and washed with several portions of hot
THF. The solvent was removed on a rotary evaporator,
and the residue was recrystallized from aqueous etha-
nol and dried in air. Yield 217 mg (0.9 mmol, 89%),
white powder, mp 133.5–134.0°C. IR spectrum, ν,
cm–1: 3650–3100 sh, 3083, 3067, 3030, 2983, 2953,
2940, 2910, 2873, 2863, 1630, 1610, 1570, 1503,
1480, 1463, 1460, 1447, 1437, 1377, 1353, 1323,
1267, 1240, 1173, 1140, 1133, 1120, 1090, 1060, 1047,
1027, 1003, 997, 970, 943, 937, 860, 847, 813, 790,
EXPERIMENTAL
The melting points were measured on a Kofler hot
stage equipped with a Hanna HI 93530 electronic
1
13
19
thermometer. The H, C, and F NMR spectra were
recorded on a Bruker Biospin Avance 500 spectrom-
eter at 500, 125, and 470 MHz, respectively, using
DMSO-d6 as solvent. The IR spectra (400–4000 cm–1)
were obtained in KBr on a Specord M-80 instrument.
The UV and fluorescence spectra were measured from
solutions in DMF or microcrystalline samples using
a Solar CM2203 spectrofluorimeter (excitation at
λ 365.0 nm). The mass spectra (atmospheric pressure
chemical ionization) were recorded on an Accela-LCQ
Fleet instrument. The solvents and reagents were puri-
fied (pure or analytical grade) and dehydrated accord-
ing to standard procedures. The progress of reactions
was monitored by TLC on silica gel 60 F254 (Merck)
applied to aluminum plates.
1
763, 747, 733. H NMR spectrum, δ, ppm: 1.41 t (3H,
CH3, J = 7.3 Hz), 4.42 q (2H, NCH2, J = 7.2 Hz),
4.67 d (4H, CH2OH, J = 5.5 Hz), 5.05 t (2H, OH, J =
5.8 Hz), 7.09 d.d (2H, 3-H, 6-H, J = 7.8, 1.3 Hz), 7.45 s
(2H, 1-H, 8-H), 7.95 d (2H, 4-H, 5-H, J = 8.0 Hz).
9-Ethyl-9H-carbazole-2,7-dicarbaldehyde (IV).
A solution of 500 mg (2.3 mmol) of pyridinium
chlorochromate in a minimal amount of 1,4-dioxane
was added dropwise under vigorous stirring to a sus-
pension of 200 mg (0.8 mmol) of diol III in anhydrous
methylene chloride, and the mixture was stirred for 8 h
at room temperature. When the initial compound dis-
appeared (TLC), excess isopropyl alcohol was added,
and the mixture was filtered through a layer of silica
gel. The solvent was removed on a rotary evaporator,
and the residue was subjected to column chromatog-
raphy on silica gel using chloroform as eluent. The
eluate was evaporated, and the product was dried
under reduced pressure. Yield 148 mg (0.6 mmol,
74%). Yellow–green crystals, mp 201.0–201.5°C. IR
spectrum, ν, cm–1: 2993, 2944, 2925, 2885, 2869,
2833, 2787, 2734, 1700, 1636, 1603, 1570, 1505, 1489,
1459, 1403, 1387, 1367, 1338, 1302, 1292, 1250, 1203,
1193, 1154, 1138, 1100, 1085, 1069, 1016, 984, 967,
Dimethyl 9H-carbazole-2,7-dicarboxylate (I) was
synthesized as described in [8].
Dimethyl 9-ethyl-9H-carbazole-2,7-dicarbox-
ylate (II). Powdered potassium carbonate, 1382 mg
(10.0 mmol), and ethyl bromide, 0.3 ml (~4.0 mmol),
were added to a solution of 285 mg (1.0 mmol) of
dimethyl 9H-carbazole-2,7-dicarboxylate (I) in
o-xylene, and the mixture was heated for 50 h under
reflux, 0.7 ml (~10.0 mmol) of ethyl bromide being
added in small portions. When the reaction was com-
plete, the solvent was removed on a rotary evaporator,
and the residue was recrystallized from benzene and
dried under reduced pressure. Yield 240 mg (0.8 mmol,
77%), mp 145.0–145.5°C. UV spectrum, λmax, nm:
256.0, 278.5, 307.5, 320.5. IR spectrum, ν, cm–1: 3107,
3093, 3043, 3027, 2997, 2977, 2910, 2897, 2867,
1723, 1707, 1637, 1610, 1577, 1503, 1487, 1477,
1457, 1443, 1433, 1383, 1373, 1347, 1333, 1290,
1
882, 869, 830, 790, 764, 757. H NMR spectrum, δ,
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 46 No. 8 2010

SYNTHESIS AND PROPERTIES OF 2,7-BIS(PHENYLETHENYL)- ...
1189
ppm: 1.47 t (3H, CH3, J = 6.5 Hz), 4.65 q (2H, NCH2,
J = 6.5 Hz), 7.77 d (2H, 3-H, 6-H, J = 8.0 Hz), 8.21 s
(2H, 1-H, 8-H), 8.37 d (2H, 4-H, 5-H, J = 8.0 Hz),
10.16 s (2H, CHO).
7.91 s (1H, 8-H), 8.20 s (1H, 1-H), 8.25 d (1H, 5-H,
J = 8.0 Hz), 8.33 d (1H, 4-H, J = 8.0 Hz), 10.14 s
(1H, CHO).
2-[(E)-2-(Benzoxazol-2-yl)ethenyl]-9-ethyl-7-
[(E)-2-phenylethenyl]-9H-carbazoles X and XI
(general procedure). Aldehyde VII or VIII, 325–
343 mg (1.0 mmol), was dissolved in DMSO, 200 mg
(1.5 mmol) of 2-methylbenzoxazole (IX) and 224 mg
(2.0 mmol) of potassium tert-butoxide were added, and
the mixture was stirred for 8 h at 40°C. When the
initial compound disappeared (TLC), the mixture was
poured into water and extracted with methylene
chloride, the solvent was removed under reduced pres-
sure, and the residue was purified by column chroma-
tography on silica gel using chloroform as eluent. The
product was additionally purified by recrystallization
from hexane and dried. Compounds X and XI were
isolated as bright yellow crystalline substances.
2-[(E)-2-(Benzoxazol-2-yl)ethenyl]-9-ethyl-7-
[(E)-2-phenylethenyl]-9H-carbazole (X). Yield
388 mg (0.9 mmol, 88%), sublimes at ~225°C. UV
spectrum, λmax, nm (ε, l mol–1 cm–1): 410.0 (68000),
429.0 (59700). Fluorescence spectrum, λmax, nm: in
solution: 472.0; in the solid state: 496.0, 544.5, 606.5.
IR spectrum, ν, cm–1: 3073, 3043, 2973, 2940, 2887,
2870, 1643, 1623, 1603, 1570, 1540, 1517, 1500,
1473, 1457, 1447, 1353, 1343, 1243, 1193, 1173,
1013, 977, 940, 853, 827, 810, 790, 773, 750, 736.
1H NMR spectrum, δ, ppm: 1.40 t (3H, CH3, J =
7.0 Hz), 4.55 q (2H, NCH2, J = 6.8 Hz), 7.25 t (2H,
m-H, J = 8.8 Hz), 7.29 t (1H, p-H, J = 7.8 Hz), 7.40 t
(1H, 5′-H or 6′-H, J = 7.3, 1.5 Hz), 7.42 d (1H, =CH,
J = 17.0 Hz), 7.42 t (1H, 6′-H or 5′-H, J = 7.5, 2.0 Hz),
7.43 d (1H, 6-H, J = 5.0 Hz), 7.51 d (1H, =CH, J =
16.5 Hz), 7.51 d (1H, 4-H or 5-H, J = 9.0 Hz), 7.65 d
(1H, 5-H or 4-H, J = 8.0 Hz), 7.71 d.d (2H, o-H, J =
8.8, 3.0 Hz), 7.74 d (1H, 4′-H or 7′-H, J = 9.0 Hz),
7.76 d (1H, 7′-H or 4′-H, J = 8.5 Hz), 7.85 s (1H, 8-H),
8.02 d (1H, =CH, J = 16.5 Hz), 8.16 d (1H, 3-H, J =
5.5 Hz), 8.18 d (1H, =CH, J = 16.0 Hz), 8.18 s (1H,
1-H). Mass spectrum: m/z 441 [M + 1]+.
9-Ethyl-7-[(E)-2-phenylethenyl]-9H-carbazole-2-
carbaldehydes VII and VIII (general procedure).
Potassium tert-butoxide, 244 mg (2.0 mmol), was
added under vigorous stirring at room temperature to
a suspension of 466–488 mg (1.2 mmol) of benzyl-
(triphenyl)phosphonium chloride V or VI in anhydrous
tetrahydrofuran. The mixture was stirred for 15–
20 min, and the resulting solution was added dropwise
to a solution of 251 mg (1.0 mmol) of dialdehyde IV
in THF. The mixture was stirred for 1 h at room tem-
perature, the progress of the reaction being monitored
by TLC. When the initial compound disappeared, the
solvent was removed on a rotary evaporator, and the
residue was purified by column chromatography on
silica gel using CH2Cl2 as eluent. The products were
isolated as yellow crystalline substances.
9-Ethyl-7-[(E)-2-phenylethenyl]-9H-carbazole-2-
carbaldehyde (VII). Yield 205 mg (0.6 mmol, 63%),
mp 185.0–186.0°C. IR spectrum, ν, cm-1: 3067, 3037,
2990, 2943, 2890, 2870, 2840, 2783, 2740, 1700,
1637, 1623, 1607, 1570, 1517, 1500, 1483, 1460,
1450, 1363, 1350, 1343, 1303, 1293, 1250, 1190,
1177, 1110, 1100, 1077, 1023, 1013, 980, 950, 917,
1
907, 880, 857, 830, 803, 787, 773, 737, 723. H NMR
spectrum, δ, ppm: 1.39 t (3H, CH3, J = 7.0 Hz), 4.58 q
(2H, NCH2, J = 7.0 Hz), 7.26 t (2H, m-H, J = 8.8 Hz),
7.30 t (1H, p-H, J = 8.3 Hz), 7.43 d (1H, =CH, J =
14.5 Hz), 7.49 d (1H, =CH, J = 16.5 Hz), 7.56 d.d (1H,
6-H, J = 8.5, 0.5 Hz), 7.72 d.d (2H, o-H, J = 8.8,
3.0 Hz), 7.75 d (1H, 3-H, J = 8.0 Hz), 7.92 s (1H,
8-H), 8.21 s (1H, 1-H), 8.26 d (1H, 5-H, J = 8.0 Hz),
8.34 d (1H, 4-H, J = 8.0 Hz), 10.14 s (1H, CHO).
9-Ethyl-7-[(E)-2-(4-fluorophenyl)ethenyl]-9H-
carbazole-2-carbaldehyde (VIII). Yield 234 mg
(0.7 mmol, 68%), mp 175.0–175.5°C. IR spectrum,
ν, cm–1: 3077, 3037, 2993, 2947, 2890, 2863, 2840,
2790, 2747, 1700, 1640, 1630, 1607, 1570, 1517,
1500, 1483, 1460, 1447, 1367, 1350, 1343, 1307,
1293, 1250, 1193, 1177, 1110, 1100, 1070, 1027, 1013,
980, 950, 920, 880, 857, 830, 817, 807, 787, 777, 740,
2-[(E)-2-(Benzoxazol-2-yl)ethenyl]-9-ethyl-7-
[(E)-2-(4-fluorophenyl)ethenyl]-9H-carbazole (XI).
Yield 417 mg (0.9 mmol, 91%), sublimes at ~230°C.
UV spectrum, λmax, nm (ε, l mol–1 cm–1): 410.0
1
727. H NMR spectrum, δ, ppm: 1.39 t (3H, CH3, J =
(62700), 429.0 (55400). Fluorescence spectrum, λmax
,
7.0 Hz), 4.58 q (2H, NCH2, J = 7.0 Hz), 7.25 d.d (2H,
m-H, JHH = JHF = 8.8 Hz), 7.42 d (1H, =CH, J =
16.5 Hz), 7.49 d (1H, =CH, J = 16.5 Hz), 7.56 d.d (1H,
6-H, J = 8.0, 0.5 Hz), 7.71 d.d (2H, o-H, JHH = 8.5,
JHF = 5.5 Hz), 7.75 d.d (1H, 3-H, J = 8.0, 0.5 Hz),
nm: in solution: 471.0; in the solid state: 510.0, 547.0,
607.5. IR spectrum, ν, cm–1: 3080, 3047, 2990, 2947,
2870, 1647, 1640, 1627, 1607, 1570, 1550, 1543,
1517, 1500, 1477, 1457, 1447, 1357, 1343, 1243,
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 46 No. 8 2010

OL’KHOVIK, BARAN
1190
1193, 1173, 1110, 1100, 1070, 1017, 980, 947, 857,
2,7-Bis[(E)-2-(benzoxazol-2-yl)ethenyl]-9-ethyl-
9H-carbazole (XIII). Potassium tert-butoxide, 338 mg
(3.0 mmol), was added under stirring to a solution of
251 mg (1.0 mmol) of dialdehyde IV and 320 mg
(2.5 mmol) of 2-methylbenzoxazole (IX) in DMSO,
and the mixture was stirred for 16 h on heating at 40–
50°C. When the initial compound disappeared (TLC),
the mixture was poured into water and extracted with
chloroform. The solvent was removed from the extract
under reduced pressure, and the product was purified
by column chromatography on silica gel using chloro-
form as eluent, followed by recrystallization from
toluene. Yield 144 mg (0.3 mmol, 76%), bright yellow
crystals, mp 309.5–312.0°C. UV spectrum, λmax, nm (ε,
l mol–1 cm–1): 389.5 (129200), 414.0 (108800). Fluo-
rescence spectrum, λmax, nm: in solution: 466.5; in the
solid state: 515.5, 548.0, 612.5. IR spectrum, ν, cm–1:
3070, 3063, 3030, 2963, 1640, 1567, 1560, 1533,
1493, 1467, 1450, 1440, 1367, 1347, 1333, 1300,
1283, 1240, 1230, 1190, 1180, 1160, 1147, 1107, 1087,
1060, 1003, 970, 930, 883, 853, 833, 823, 817, 797,
1
827, 810, 803, 787, 773, 757. H NMR spectrum, δ,
ppm: 1.40 t (3H, CH3, J = 7.0 Hz), 4.55 q (2H, NCH2,
J = 7.0 Hz), 7.25 d.d (2H, m-H, JHH = JHF = 9.0 Hz),
7.40 t (1H, 5′-H or 6′-H, J = 7.5, 1.5 Hz), 7.42 d (1H,
=CH, J = 17.0 Hz), 7.42 t (1H, 6′-H or 5′-H, J = 7.5,
1.8 Hz), 7.43 d (1H, 6-H, J = 5.0 Hz), 7.51 d (1H,
=CH, J = 16.5 Hz), 7.51 d (1H, 4-H or 5-H, J =
8.5 Hz), 7.65 d (1H, 5-H or 4-H, J = 8.0 Hz), 7.71 d.d
(2H, o-H, JHH = 8.5, JHF = 5.5 Hz), 7.74 d (1H, 4′-H or
7′-H, J = 9.0 Hz), 7.76 d (1H, 7′-H or 4′-H, J =
8.5 Hz), 7.85 s (1H, 8-H), 8.02 d (1H, =CH, J =
16.0 Hz), 8.16 d (1H, 3-H, J = 5.0 Hz), 8.18 d (1H,
19
=CH, J = 16.5 Hz), 8.18 s (1H, 1-H). F NMR spec-
trum: δF –114.65 ppm, d.t (J = 9.4, 4.9 Hz). Mass spec-
trum: m/z 459 [M + 1]+.
9-Ethyl-2-[(E)-2-(p-fluorophenyl)ethenyl]-7-[(E)-
2-phenylethenyl]-9H-carbazole (XII). Benzyl(tri-
phenyl)phosphonium chloride (V), 466 mg
(1.2 mmol), was dispersed in anhydrous tetrahydro-
furan, 244 mg (2.0 mmol) of potassium tert-butoxide
was added under vigorous stirring at room tempera-
ture, and the mixture was stirred for 15–20 min. The
resulting ylide solution was added dropwise to a solu-
tion of 325 mg (1.0 mmol) of carbazole-2-carbalde-
hyde VIII in THF, and the mixture was stirred for 1 h
at room temperature, the progress of the reaction being
monitored by TLC. When the initial compound disap-
peared, the mixture was filtered through a layer of
silica gel, and the product was purified by column
chromatography on silica gel using toluene as eluent,
followed by recrystallization from toluene. Yield
384 mg (0.9 mmol, 92%), light yellow crystals,
mp 256.0–257.5°C. UV spectrum, λmax, nm (ε, l×
mol–1 cm–1): 384.0 (23500), 401.5 (20700). Fluores-
cence spectrum, λmax, nm: in solution: 434.0; in the
solid state: 456.0, 489.5. IR spectrum, ν, cm–1: 3067,
3037, 2987, 2977, 2937, 1630, 1600, 1567, 1560,
1507, 1493, 1470, 1450, 1440, 1350, 1333, 1323,
1237, 1190, 1170, 1133, 1107, 1093, 1063, 1040, 1010,
973, 880, 853, 830, 823, 810, 800, 777, 770, 757, 737,
730, 700. 1H NMR spectrum, δ, ppm: 1.39 t (3H, CH3,
J = 7.3 Hz), 4.55 q (2H, NCH2, J = 6.8 Hz), 7.25 d.d
(2H, m-H, JHH = JHF = 9.0 Hz), 7.28 t (1H, p′-H, J =
8.0 Hz), 7.38–7.43 m (4H, =CH), 7.44 d (2H, 3-H,
6-H, J = 6.5 Hz), 7.49 t (2H, m′-H, J = 8.0 Hz), 7.66 d
(2H, o′-H, J = 7.5 Hz), 7.70 d.d (2H, o-H, JHH = 8.3,
1
783, 757, 737, 723, 703. H NMR spectrum, δ, ppm:
1.41 t (3H, CH3, J = 7.0 Hz), 4.60 t (2H, NCH2, J =
7.5 Hz), 7.40 d.t (2H, 5′-H or 6′-H, J = 7.3, 1.3 Hz),
7.43 d.t (2H, 6′-H or 5′-H, J = 7.5, 1.5 Hz), 7.54 d (2H,
=CH, J = 16.5 Hz), 7.67 d.d (2H, 3-H, 6-H, J = 8.5,
1.0 Hz), 7.75 d.d (2H, 4′-H or 7′-H, J = 8.5, 0.5 Hz),
7.76 d.d (2H, 7′-H or 4′-H, J = 8.5, 0.5 Hz), 8.03 d
(2H, =CH, J = 16.0 Hz), 8.19 s (2H, 1-H, 8-H), 8.25 d
(2H, 4-H, 5-H, J = 8.0 Hz). Mass spectrum: m/z 482
[M + 1]+.
2,7-Bis[(E)-2-phenylethenyl]-9-ethyl-9H-carba-
zoles XIV and XV (general procedure). Potassium
tert-butoxide, 366 mg (3.0 mmol), was added to a sus-
pension of 972–1017 mg (2.5 mmol) of benzyl(tri-
phenyl)phosphonium chloride V or VI in anhydrous
tetrahydrofuran under vigorous stirring at room tem-
perature. The mixture was stirred for 15–20 min,
a solution of 251 mg (1.0 mmol) of 9-ethyl-9H-carba-
zole-2,7-dicarbaldehyde (IV) in THF was added drop-
wise at room temperature to the resulting phosphonium
ylide solution, and the mixture was stirred for 1 h at
room temperature, the progress of the reaction being
monitored by TLC. When the initial compound
disappeared, the mixture was filtered through a layer
of silica gel, and the product was purified by column
chromatography on silica gel using toluene as eluent,
followed by recrystallization from toluene. Com-
pounds XIV and XV were isolated as light yellow
crystalline substances.
J
HF = 5.8 Hz), 7.82 s (1H, 1-H or 8-H), 7.84 s (1H, 9-H
19
or 1-H), 8.12 d (2H, 4-H, 5-H, J = 8.0 Hz). F NMR
spectrum: δF –114.80 ppm, d.t (J = 9.3, 5.2 Hz). Mass
spectrum: m/z 418 [M + 1]+.
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 46 No. 8 2010

SYNTHESIS AND PROPERTIES OF 2,7-BIS(PHENYLETHENYL)- ...
1191
9-Ethyl-2,7-bis[(E)-2-phenylethenyl]-9H-carba-
zole (XIV). Yield 272 mg (0.7 mmol, 68%),
mp 241.0–242.5°C. UV spectrum, λmax, nm (ε, l×
mol–1 cm–1): 369.0 (59500), 387.0 (54500). Fluores-
cence spectrum, (in solution): λmax 435.5 nm. IR spec-
trum, ν, cm–1: 3090, 3067, 3043, 2977, 2943, 2870,
1607, 1516, 1463, 1423, 1307, 1267, 1240, 1210, 1170,
1140, 1110, 1090, 1027, 980, 970, 950, 856, 773.
1H NMR spectrum, δ, ppm: 1.39 t (3H, CH3, J =
7.5 Hz), 4.55 q (2H, NCH2, J = 7.0 Hz), 7.26 t (2H,
p-H, J = 8.5 Hz), 7.34 d (2H, =CH–, J = 16.5 Hz),
7.37 t (4H, m-H, J = 7.5 Hz), 7.42 d (2H, 3-H, 6-H, J =
8.0 Hz), 7.45 d (2H, =CH, J = 16.5 Hz), 7.65 d.d (2H,
o-H, J = 8.3, 2.0 Hz), 7.84 s (2H, 1-H, 8-H), 8.10 d
(2H, 4-H, 5-H, J = 8.0 Hz). Mass spectrum: m/z 400
[M + 1]+.
7.0 Hz), 7.25 d.d (4H, m-H, JHH = JHF = 8.8 Hz), 7.33 d
(2H, =CH–, J = 16.5 Hz), 7.43 d (2H, 3-H, 6-H, J =
8.0 Hz), 7.45 d (2H, =CH–, J = 16.5 Hz), 7.70 d.d (2H,
o-H, JHH = 8.5, JHF = 5.5 Hz), 7.82 s (2H, 1-H, 8-H),
8.11 d (2H, 4-H, 5-H, J = 8.0 Hz). Mass spectrum:
m/z 436 [M + 1]+.
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9-Ethyl-2,7-bis[(E)-2-(4-fluorophenyl)ethenyl]-
9H-carbazole (XV). Yield 276 mg (0.6 mmol, 64%),
mp 235.5–236.0°C. UV spectrum, λmax, nm (ε, l×
mol–1 cm–1): 365.0 (44200), 382.0 (39800). Fluores-
cence spectrum, λmax, nm: in solution: 424.5; in the
solid state: 437.0, 449.0. IR spectrum, ν, cm–1: 3073,
3040, 2943, 2873, 1600, 1573, 1510, 1470, 1453,
1433, 1377, 1360, 1340, 1323, 1307, 1237, 1207,
1170, 1160, 1120, 1087, 1040, 997, 977, 923, 893, 883,
5. Thomas, K.R.J., Lin, J.T., Tao, Y.-T., and Ko, Ch.-W.,
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chyts, G.V., Matveienko, Y.V., Baran, A.G., Hali-
nouski, N.A., and Petushok, V.G., Arkivoc, 2008,
part (ix), p. 69.
1
853, 820, 763, 737, 703. H NMR spectrum, δ, ppm:
1.39 t (3H, CH3, J = 7.5 Hz), 4.55 q (2H, NCH2, J =
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 46 No. 8 2010